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ipc/sem.c: sem use list operations

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Replace the handcoded list operations in update_queue() with the standard
list_for_each_entry macros.

list_for_each_entry_safe() must be used, because list entries can
disappear immediately uppon the wakeup event.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin 2009-12-15 16:47:29 -08:00 committed by Linus Torvalds
parent bf17bb7177
commit 9cad200c76
1 changed files with 31 additions and 44 deletions
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75
ipc/sem.c
View file

@ -403,58 +403,45 @@ undo:
*/
static void update_queue (struct sem_array * sma)
{
int error;
struct sem_queue * q;
struct sem_queue *q, *tq;
again:
list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {
int error;
int alter;
q = list_entry(sma->sem_pending.next, struct sem_queue, list);
while (&q->list != &sma->sem_pending) {
error = try_atomic_semop(sma, q->sops, q->nsops,
q->undo, q->pid);
/* Does q->sleeper still need to sleep? */
if (error <= 0) {
struct sem_queue *n;
if (error > 0)
continue;
/*
* Continue scanning. The next operation
* that must be checked depends on the type of the
* completed operation:
* - if the operation modified the array, then
* restart from the head of the queue and
* check for threads that might be waiting
* for semaphore values to become 0.
* - if the operation didn't modify the array,
* then just continue.
* The order of list_del() and reading ->next
* is crucial: In the former case, the list_del()
* must be done first [because we might be the
* first entry in ->sem_pending], in the latter
* case the list_del() must be done last
* [because the list is invalid after the list_del()]
*/
if (q->alter) {
list_del(&q->list);
n = list_entry(sma->sem_pending.next,
struct sem_queue, list);
} else {
n = list_entry(q->list.next, struct sem_queue,
list);
list_del(&q->list);
}
list_del(&q->list);
/* wake up the waiting thread */
q->status = IN_WAKEUP;
/*
* The next operation that must be checked depends on the type
* of the completed operation:
* - if the operation modified the array, then restart from the
* head of the queue and check for threads that might be
* waiting for semaphore values to become 0.
* - if the operation didn't modify the array, then just
* continue.
*/
alter = q->alter;
wake_up_process(q->sleeper);
/* hands-off: q will disappear immediately after
* writing q->status.
*/
smp_wmb();
q->status = error;
q = n;
} else {
q = list_entry(q->list.next, struct sem_queue, list);
}
/* wake up the waiting thread */
q->status = IN_WAKEUP;
wake_up_process(q->sleeper);
/* hands-off: q will disappear immediately after
* writing q->status.
*/
smp_wmb();
q->status = error;
if (alter)
goto again;
}
}